Microstructure And Properties Of Nanocrystalline Cu-Nbc Composites And Copper Bulks Prepared By Power Metallurgy

Copper alloys have been widely used as high-speed railway contact wire,integrated circuit lead frame,high magnetic fields conductor,electric motor rotator and resistance welding electrode due to its superior strength,electrical conductivity,ductility and temperature resistance.With the unceasing paces of development modern industry,copper alloys with more excellent properties are expected to satisfy the increasingly stringent requirements in different fields;however,strategies to strengthen the materials by introducing obstacles to the motion of dislocations often cause deteriorating of the electrical conductivity and ductility,which makes it necessary to make a trade-off when developing copper and copper alloys.In this study,nanocrystalline Cu-6.4 vol.% NbC composites and copper bulks are prepared by powder metallurgy methods including high energy mechanical milling(HEMM)and thermomechanical consolidation and spark plasma sintering(SPS),respectively.Microstructure of the materials are characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and the properties are measured by tensile tests,hardness tests and electrical resistivity tests.Based on the linking of theory and practice,conclusions can be drawn as follows:(1)Nanocrystalline Cu-6.4 vol.% NbC composites with superior strength and electrical conductivity are achieved by combining high energy mechanical milling,vacuum sintering and hot extrusion;(2)An addition(0.1 wt.%)of doping elements like Al,Ti and Zr can further strengthen and stabilize the materials while maintaining a high electrical conductivity by suppressing the growth of Cu grains and NbC nanoparticles;(3)Pre-annealing of the copper powders under hydrogen can effectively facilitate the consolidation during spark plasma by removing the oxide layer on the powders;(4)An increasing amount of nano-sized powders can improve the nucleation ratio during recrystallization in the SPS process which results in a smaller grain size that strengthens the materials;while the micro-sized powders provide space for the dislocation pile-ups and inhibits the propagation of the cracks and thereby improve the ductility of the materials;(5)By tailoring the volume fraction of the nano-sized and micro-sized powders,one can make a good trade-off between the strength and ductility of the materials.